Engine manufacturers have developed techniques for constantly monitoring the operational characteristics of the engine to determine when engine operation is abnormal or outside of prescribed tolerances. Engine manufactures have sought approaches and methods to determine or predict when abnormal operations may occur in an attempt to meet the demand for increased internal combustion engine efficiency and improved emissions control. Similarly, having approaches that may identify early anomalies in operations may assist in preventing damage and avoiding potentially costly repairs to an internal combustion engine
Engine cylinder misfire (i.e., misfire) is an example of one such event. Engine manufacturers seek to detect the occurrence of a misfire, for when detected, a misfire may be an early indication of a potential problem with the operation of the engine. For instance, a cylinder misfire can occur due to failed ignition of the fuel-air mixture within an engine cylinder (lack of combustion) or the incomplete ignition of the fuel-air mixture caused by too lean of a mixture (incomplete combustion). In operation, where such a misfire occurs, the affected engine performance is diminished, emissions are likely increased, and fuel economy is reduced. Similarly, if left uncorrected, a misfire may also result in damage to the engine and its components, including damage to the catalytic converter, for instance.
Further, engine cylinder misfire detection is a requirement for On-Board Diagnostics II (OBD II). OBD II is a second generation of on-board self-diagnostic equipment requirements which provide for the ability to monitor engine components that can affect emission performance, such as misfires in engines. Typically, an OBD II system will also store important information about a detected malfunction, such as engine cylinder misfire and the faulted cylinder or component.
Engine manufacturers have used a variety of approaches to detect engine misfires, but none of the prior art methods take into account a multitude of present operating conditions of an internal combustion engine including exhaust manifold pressure (EMP) with information from other sensor data such as engine speed, charge flow (or mass air flow (MAF)), Exhaust gas Recirculation (EGR) pressure, ambient pressure, turbine speed and turbine position, to detect an engine misfire.
For example, U.S. Pat. No. 5,193,513 to Marko et al. discloses a misfire detection system for use in an internal combustion engine in which an exhaust pressure sensor, a position sensor for sensing the rotational position of the engine, and an analog-to-digital converter for digitizing an analog signal received from the pressure sensor are employed. The digitized pressure data is compared using a data classifier (i.e. pattern recognition system) that is trained to recognize data signatures of individually misfiring cylinders. To train the classifier, the engine is operated in a service bay and engine data is collected during both intentionally induced misfires and under normal conditions. This data is then presented to the data classifier in a training operation. Engine misfire detection systems such as the one disclosed in Marko, et al., however, fail to compare a multitude of engine operation characteristics to sensed engine cylinder peak pressures as a way of detecting partial or complete engine misfires.
U.S. Pat. No. 3,965,677 to Goto et al. discloses a misfire detecting apparatus in which the suction pressure of an engine is detected and used to calculate a threshold level wherein a cylinder misfire is declared if the exhaust gas pressure exceeds this threshold level.
U.S. Pat. No. 3,983,754 to Deguchi et al. discloses an apparatus for detecting misfires in a multi-cylinder internal combustion engine in which pressure responsive devices are provided in the branches of the exhaust manifold or exhaust ports and the outputs of these devices are compared to detect an engine cylinder misfire.
U.S. Pat. No. 4,567,755 to Ootsuka et al. discloses an ignition/misfire detector for an internal combustion engine in which a pressure detection unit is used to detect changes in combustion pressure in the engine and an ignition/misfire detection unit is used to determine the occurrence of an engine ignition misfire.
U.S. Pat. No. 3,924,457 to Oshima et al. discloses a misfire detecting device for an internal combustion engine in which an exhaust gas introducing tube is provided adjacent to an exhaust port in an exhaust passage to provide exhaust gas to a pressure transducer disposed at one end of the exhaust gas introducing tube to determine pressure fluctuation which may indicate a possible engine cylinder misfire.
In OBD II systems, many current monitors use crank speed fluctuations in order to detect misfires. However, it is generally recognized that using crank speed fluctuations are dependent upon power train and vehicle dynamics. Such dependency, including that using engine speed, is limiting however as the portability of detection across various applications is unavailable and the inputted data is often negatively influenced by driveline dynamics.
These prior methods of detecting engine cylinder misfire are devoid of the unique approach to employ a multitude of present engine operating conditions, including that of utilizing a relationship between in-cylinder pressure, changes in EMP fluctuations and other operating conditions to provide an efficient engine cylinder misfire detection system.
A novel engine cylinder misfire detection system and improvement over the prior art is disclosed in U.S. Pat. No. 5,392,642 to Tau, a patent which is assigned to Cummins Engine Company, Inc., the same assignee of the present invention. This patent discloses an engine cylinder misfire system that uses a sensor to monitor an engine cylinder for all engine cycles and to provide an average of the detected output for each cylinder. Furthermore, the engine speed and fuel rate of the internal combustion engine are used to provide a more effective engine cylinder misfire detection system. Nevertheless, the invention disclosed in the Tau patent is directed to a system for detecting low power in at least one cylinder of a multi-cylinder engine. Furthermore, this application discloses the use of multiple pressure sensors, specifically one sensor for each cylinder to provide engine misfire detection.
A further novel engine cylinder misfire detection system and improvement over the prior art is disclosed in U.S. Pat. No. 6,243,641 to Andrews et al., incorporated herein by reference, which is a patent assigned to Cummins Engine Company, Inc., the same assignee of the present invention. This patent discloses an engine cylinder misfire detector system which calculates and compares a minimum pressure value, using a pressure sensing means for sensing the peak pressure of the exhaust gas flowing through the exhaust and operating characteristics of the internal combustion engine, to determine if an engine cylinder misfire has occurred.
Other approaches have also been set forth, but these methods also are devoid of detecting engine cylinder misfire utilizing a relationship between in-cylinder pressure, changes in EMP fluctuations and other operating conditions to provide an efficient engine cylinder misfire detection system that it operable over a variety of operating environments (i.e., power trains, vehicles, etc.), may be calibrated across different applications, and is reliable over a variety of operating conditions.
Therefore, the inventor has recognized a need for an engine cylinder misfire detection system that detects changes in EMP fluctuations, compares the EMP fluctuations with diagnostic thresholds determined with other information obtained from other engine sensor data, and determines whether a cylinder misfire has occurred. Further, the inventor has recognized a need for developing a method of monitoring and detecting EMP fluctuations to determine the occurrence of a misfire.